Recently, so-called social network games have become widespread as applications executable in a social networking service (SNS).
According to the social network games, besides collaborative play with other users (friends), users exchange information through communication with friends such as greetings and contacts, and give or exchange items in the game with friends. As an example of the social network games, a digital card game (Dragon collection (registered trademark)) is disclosed in a Japanese game magazine “Appli Style, Vol. 5 (Eastpress Co., Ltd.) p. 7-8.”